Cache last commit to accelerate the repository directory page visit (#10069)

* Cache last commit to accelerate the repository directory page visit

* Default use default cache configuration

* add tests for last commit cache

* Simplify last commit cache

* Revert Enabled back

* Change the last commit cache default ttl to 8760h

* Fix test

modules/cache/last_commit.go

@@ -0,0 +1,64 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package cache
+
+import (
+	"fmt"
+
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+
+	mc "gitea.com/macaron/cache"
+	"gopkg.in/src-d/go-git.v4/plumbing/object"
+)
+
+// LastCommitCache represents a cache to store last commit
+type LastCommitCache struct {
+	repoPath    string
+	ttl         int64
+	repo        *git.Repository
+	commitCache map[string]*object.Commit
+	mc.Cache
+}
+
+// NewLastCommitCache creates a new last commit cache for repo
+func NewLastCommitCache(repoPath string, gitRepo *git.Repository, ttl int64) *LastCommitCache {
+	return &LastCommitCache{
+		repoPath:    repoPath,
+		repo:        gitRepo,
+		commitCache: make(map[string]*object.Commit),
+		ttl:         ttl,
+		Cache:       conn,
+	}
+}
+
+// Get get the last commit information by commit id and entry path
+func (c LastCommitCache) Get(ref, entryPath string) (*object.Commit, error) {
+	v := c.Cache.Get(fmt.Sprintf("last_commit:%s:%s:%s", c.repoPath, ref, entryPath))
+	if vs, ok := v.(string); ok {
+		log.Trace("LastCommitCache hit level 1: [%s:%s:%s]", ref, entryPath, vs)
+		if commit, ok := c.commitCache[vs]; ok {
+			log.Trace("LastCommitCache hit level 2: [%s:%s:%s]", ref, entryPath, vs)
+			return commit, nil
+		}
+		id, err := c.repo.ConvertToSHA1(vs)
+		if err != nil {
+			return nil, err
+		}
+		commit, err := c.repo.GoGitRepo().CommitObject(id)
+		if err != nil {
+			return nil, err
+		}
+		c.commitCache[vs] = commit
+		return commit, nil
+	}
+	return nil, nil
+}
+
+// Put put the last commit id with commit and entry path
+func (c LastCommitCache) Put(ref, entryPath, commitID string) error {
+	log.Trace("LastCommitCache save: [%s:%s:%s]", ref, entryPath, commitID)
+	return c.Cache.Put(fmt.Sprintf("last_commit:%s:%s:%s", c.repoPath, ref, entryPath), commitID, c.ttl)
+}